Download File - Tigard High Automotive Technology

THS
Automotive
Technology
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Components of an Electrical Circuit
THS
Automotive
Technology
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Factors that influence resistance
• The five factors that determine the resistance of
conductors are length, diameter, temperature, physical
condition, and conductor material. A light bulb filament,
motor windings or coil windings, and the bimetal elements
in sensors are conductors. Also, the five factors apply to
circuit wiring and working devices or loads.
When two wires consist of the same material and diameter,
the longer wire has greater resistance than the shorter wire.
Wire resistance is listed in ohms per foot. Replacement
wires must be the proper length.
THS
Automotive
Technology
Factors that influence resistance
If two wires are the same material and length, the thinner
wire has greater resistance than the thicker wire. Wire
resistance tables list ohms per foot for wires of varying
thicknesses. Replacement wires and splices must be the
proper size for the circuit current.
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
NOTE: Consider size and gauge when replacing wires.
Those with 1, 2, and 3 are thicker with less resistance and
more current capacity while those with 18, 20, and 22 are
thinner with more resistance and less current capacity.
THS
Automotive
Technology
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Factors that influence resistance
In most conductors, resistance increases as wire
temperature increases because electrons move faster
and create heat. In most insulators, resistance
decreases as temperature increases. Various test
equipment can be used to measure temperature and
resistance.
THS
Automotive
Technology
Factors that influence resistance
Partially nicked or cut wire has high resistance in the
damaged area. A kink in the wire, poor splices, and
loose or corroded connections also increase resistance.
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Materials with free electrons
are good conductors and
have low resistance to
current flow. Materials with
bound electrons are
insulators (poor conductors)
and have high resistance to
current flow.
NOTE: Copper, aluminum, gold, and silver are good
conductors. Rubber, glass, paper, ceramics, plastics, and
air are insulators.
THS
Automotive
Technology
Stranded wire
• The stranded-wire conductor uses wire made from copper
covered with polyvinyl chloride (PVC) insulation. The PVC
insulation prevents electrical shorts because the bare
electrical wire does not touch other conductive materials.
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Circuit wires must have enough surface area to carry the
amount of current needed to operate the load properly.
Also, they must withstand vibration and bending.
Stranded wire is rated according to the highest electrical
current the wire can take without becoming too hot.
Length helps determine wire size. The greater the distance
from the source of electrical current, the greater the resistance
to current flow. Larger sizes of wire can counter this resistance
by providing a greater number of current paths to the load.
THS
Automotive
Technology
Electrical Circuits
Stranded wire
The American Wire Gauge System (AWGS) and the Metric
Wire Gauge System (MWGS) are used to size wire. Both of
these systems assign an identification number to electrical
wire based upon wire diameter.
• In the AWGS, the larger the number, the smaller the wire
size. Identification numbers range from 22 gauge (small)
to 000 gauge (large). The cross-section of a wire is
measured in a unit called a circular mil, which is the
equivalent area of a circle whose diameter is 0.001 in.
Lesson 1:
Components of
an Electrical Circuit
• In the MWGS, the larger the number, the larger the wire
size. Identification numbers range from 0.5 millimeters
(small) to 4.0 millimeters (large).
Individual wires are bound into wiring harnesses and routed
throughout the vehicle. For an orderly wiring system,
manufacturers cover wires with different insulation colors.
THS
Automotive
Technology
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Stranded wire
• The printed circuit board is a conductor. Copper is
laminated to an insulating material. The copper is
processed so that it forms individual strips, each of which
becomes a current path for circuits.
THS
Automotive
Technology
Stranded wire
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
NOTE: The copper strips in printed circuit boards are thin
and should be handled with care. Check for breaks in the
printed circuit board where there is a bend.
THS
Automotive
Technology
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Stranded wire
• If the body of the vehicle is constructed of metal, it can be a
conductor. To cut costs and reduce vehicle weight,
manufacturers use the steel frame and metal body as a
current path for some circuits. This is referred to as chassis
ground or a 1-wire system.
THS
Automotive
Technology
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Stranded wire
• In early model cars, spark plugs were made of stranded
copper wrapped in thick insulation. When radios were
introduced, a change in spark plug wire construction
became necessary.
The force of electron flow is so great in spark plug wires
that it causes a popping noise in the radio. To eliminate
this noise, manufacturers use radio suppression wires in
spark plugs.
• Radio suppression wires are fiberglass cords saturated
with carbon. Heavy silicone or vinyl insulates the central
cord.
• Because carbon is not as good of a conductor as
copper, radio suppression wires generate less radio
interference.
THS
Automotive
Technology
Stranded wire
Special care should be taken when removing and installing
spark plug wires. If stretched, the fiberglass cord within the
spark plug wire can be easily damaged.
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
• Carbon is used in a
variety of conductors. It
has a higher resistance
to current flow than
other conductors. Also,
carbon can maintain
current flow between
stationary and rotating
parts and resist wear
that results from
rubbing.
THS
Automotive
Technology
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Types of electrical insulation
• Electrical insulation keeps electron flow inside the
conductor and prevents different conductors from making
contact. PVC is the most common type of electrical
insulation.
NOTE: Insulation devices can be deceptive. A flat washer
can be an insulation device. The technician must know
where current Is supposed to flow within a circuit.
• Glass and porcelain are
used as insulation devices
because they maintain
resistance at high
temperatures. These
materials are used in spark
plugs, oxygen sensors,
and other applications that
involve high temperatures
and high voltage.
THS
Automotive
Technology
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Types of electrical insulation
• Bakelite, plastic, and alkyd are used as rigid insulation
devices because they can be molded into almost any
shape. A conductor can be embedded into these materials
or placed in them after molding. The following are
examples of how rigid insulation devices are used in
different areas of the vehicle.
THS
Automotive
Technology
Types of electrical insulation
• Insulating washers prevent current from grounding as it
passes through other conductive materials. The following
shows a stud inserted through the aluminum housing of
an alternator. The insulating washers keep the stud from
contacting the aluminum housing.
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
• Conductors that lie close to each other are often coated
with varnish to ensure that current does not leak from one
conductor to the other. Any wrapped coil is coated with
varnish.
THS
Automotive
Technology
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Types of circuit protection devices
• Fuses, fusible links, and circuit breakers are located in the
fuse block. These devices are designed to open the circuit
when excess current flows through.
THS
Automotive
Technology
Types of circuit protection devices
• The fuse is a zinc strip bonded between two endcaps.
The zinc strip is encased in glass, plastic, or a ceramic
sleeve. It is designed to destruct at a specific ampere of
current flow.
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Autofuse
Maxifuse
Minifuse
THS
Automotive
Technology
Types of circuit protection devices
Fuses are categorized by a letter system and number. The
number indicates the maximum current-carrying capacity.
The appearance of a blown fuse can indicate the cause of
a circuit overload.
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
• Small breaks in the zinc strip indicate a high-voltage
surge or momentary current overload.
• Large breaks in the zinc strip indicate a high-current
overload, grounded conductor, or shorted load.
• Vaporized breaks in the zinc strip indicate a grounded
circuit.
THS
Automotive
Technology
Types of circuit protection devices
• The fusible link is a short piece of alloyed wire. The alloy
causes the fusible link to destruct at a specific ampere of
current flow.
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Fusible links are rated by wire gauge size and amperes.
Fusible links are usually located near the terminal
connection to the power source. Fusible links sometimes
have a molded flag at the terminal end, indicating gauge
size and ampere rating.
Locating a blown fusible link can be difficult. Insulation
surrounding a destroyed fusible link appears undamaged
even though the insulation can be somewhat soft. The break
can be located by squeezing or pulling gently on the wire.
THS
Automotive
Technology
Types of circuit protection devices
CAUTION: Do not bypass a blown fusible link to
restore a circuit. Replace the fusible link with wire
that is the correct gauge and appropriate length.
• The circuit breaker is a thermally operated device.
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
A bimetal strip keeps contact points on the circuit breaker
closed.
• When current flow through the bimetal strip becomes
too great, it overheats and bends to open the contact
point and disrupt circuit operation.
• When the bimetal strip cools, it contracts and closes
the contacts to reactivate the circuit.
THS
Automotive
Technology
Types of circuit protection devices
• If circuit overload persists, the circuit breaker again
overheats and opens, causing the circuit to be
intermittently on and off. Continuous action of the circuit
breaker can result in premature failure.
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Circuit breakers are rated according to their maximum
current draw before opening.
THS
Automotive
Technology
Types of circuit protection devices
Manual circuit breakers can be reset in two ways. One way
is to push a button located on the circuit breaker. The other
way is to disconnect power to the circuit breaker and wait for
it to cool down.
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
The positive temperature coefficient (PTC)
circuit breaker is wired inside a load component
like a wiper motor or power window motor.
When current exceeds design limits, resistance
of the PTC circuit breaker increases until the
circuit is opened. The PTC circuit breaker
resets once the high current condition of the
circuit is no longer present.
THS
Automotive
Technology
Circuit load devices and how they function
• An electrical component must meet three requirements to
be considered a load device.
The device must have some current resistance to ensure
the force device is not depleted too rapidly.
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
The resistance of a load device must not be great enough
to prevent current flow within the circuit.
The load must perform some observable function, such as
producing light, heat, or magnetism.
THS
Automotive
Technology
Circuit load devices and how they function
• Incandescent bulbs are the most common source of light in
a vehicle. Incandescent bulbs are illumination loads.
Incandescent bulbs are either single filament or multiple
filament.
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
• A single-filament incandescent bulb has one insulated
contact. The bulb is grounded through its socket. In a
smaller single-filament bulb, a separate contact
provides ground.
• A multiple-filament incandescent bulb has two heating
filaments. It is grounded by a socket or by a separate
terminal or contact.
THS
Automotive
Technology
Circuit load devices and how they function
A numbering system categorizes incandescent bulbs
according to their use.
The lower the resistance of a filament, the greater the
current flow through it and the brighter the light produced.
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
THS
Automotive
Technology
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Circuit load devices and how they function
• Wound coils are known as coil-wrapped loads. These are
used in electrical load devices, such as starters, relays,
ignition coils, wiper motors, gauges, and alternators. Wound
coils function according to three basic magnetic principles.
If a current is being forced through a conductor, a magnetic
field is created around that conductor.
To increase the strength of the magnetic field, the conductor
is wrapped into a coil. Also, increasing current flow through
the conductor or placing an iron core within the coil
increases the strength of the magnetic field.
A wrapped conductor that produces a magnetic field when
current passes through it is a load device.
THS
Automotive
Technology
Circuit load devices and how they function
• The maximum current-carrying capacity of some
conductors is balanced with the amount of heat the
conductor can safely handle. The conductor produces heat
as current flows. These conductors are known as thermal
loads.
Electrical Circuits
Nichrome is the most common type of thermal load. It can
produce intense heat from large amounts of current flow
without sustaining damage.
Lesson 1:
Components of
an Electrical Circuit
The heat produced by thermal loads can perform a variety
of functions, such as defrosting windows and operating
warning gauges.
THS
Automotive
Technology
Electrical Circuits
Capacitors and how they function
• A capacitor uses an electrostatic field to absorb or store an
electrical charge.
A capacitor in a circuit builds up a charge on its negative
plate. Current flows until the capacitor charge and power
source are equal. The capacitor charge is then stored until it
is discharged through another circuit.
CAUTION: Handle capacitors with care. Once charged,
they can cause shocks long after power is removed.
Lesson 1:
Components of
an Electrical Circuit
• The three types of capacitors are the ceramic, paper and
foil, and electrolytic.
The ceramic capacitor is used for electronic circuits.
THS
Automotive
Technology
Capacitors and how they function
The paper and foil capacitor is used for noise containment
in charging and ignition systems.
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
The electrolytic capacitor is used for turn signal lights.
THS
Automotive
Technology
Capacitors and how they function
• Capacitors are rated in microfarads. The rating is stamped
on the case. Make sure to choose the proper capacitor rated
for the maximum expected voltage.
Capacitance
Electrical Circuits
Symbol
Pronounced as
Lesson 1:
Components of
an Electrical Circuit
Multiplier
Basic Unit
Units for Small Values
F
µF
pF
Farad
Microfarad
Picofarad
1
1x10-6
(1/1,000,000)
1x10-12
(1/1,000,000,000,000)
THS
Automotive
Technology
Electrical Circuits
Capacitors and how they function
• A resistor is a mechanical or semiconductor device that
reduces the electrical force in a circuit. All loads reduce
electrical force to some degree.
The force reduction across a load is called voltage drop.
When electrons are forced through a coil, light bulb, or heater,
they are converted into magnetism, heat, light, or motion.
Lesson 1:
Components of
an Electrical Circuit
The resistor cases voltage drop to occur across itself. It
differs from other load devices because its single purpose is
to produce voltage drop, causing the circuit to operate at
lower voltage.
NOTE: Heat and magnetism produced by the resistor have
no practical use.
THS
Automotive
Technology
Capacitors and how they function
The three classifications of resistors are fixed-value,
stepped, and variable.
• The two types of fixed-value resistors are wire-wound
and carbon.
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Wire-wound resistors are made with coils of
resistor wire. They are accurate and heat stable.
The resistance value is marked on them.
THS
Automotive
Technology
Electrical Circuits
Capacitors and how they function
Carbon resistors are mixed with binder. The more
carbon, the lower the resistance. Some have the
resistance value stamped on them while others are
rated in watts of power. Most have color-coded bands
to show resistance value. A carbon resistor with four
bands – red, green, black, and brown from left to right
– is sized as follows:
• The first two bands set the digits. Red is 2 and
green is 5.
Lesson 1:
Components of
an Electrical Circuit
• The next band represents the number of zeros.
Black is 0 zeros. So, the resistor has a base
value of 25W.
• The last band represents tolerance. Brown is 1%.
So, the resistance value is 25 ohms plus or minus
.25 ohms, or 24.75W to 25.25W.
THS
Automotive
Technology
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Capacitors and how they function
THS
Automotive
Technology
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Capacitors and how they function
• Two or more fixed resistance values are contained in
stepped or tapped resistors. The different resistances,
which are either carbon or wire, are connected to different
terminals in a switch. Different resistance values are placed
in the circuit as the switch is moved.
THS
Automotive
Technology
Electrical Circuits
Capacitors and how they function
• The three types of variable resistors are rheostats,
potentiometers, and thermistors.
The rheostat dims or brightens the dash panel lighting
and is located on the headlight switch. One end of the
rheostat is connected to the fixed end of a resistor. The
other end is connected to a sliding contact on the resistor.
Rotating the control increases or decreases resistance.
Lesson 1:
Components of
an Electrical Circuit
The potentiometer is a device that varies resistance
according to the movement of mechanical parts. The first
two connections of a potentiometer are made at each of the
resistor ends. The last connection is made on a sliding
contact. Rotating the control increases or decreases
resistance in the circuit.
THS
Automotive
Technology
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Capacitors and how they function
The thermistor is a device that varies resistance according
to temperature. Negative temperature coefficient (NTC)
thermistors and positive temperature coefficient (PTC)
thermistors can be used in the same vehicle.
• Each of these thermistors change resistance with an
increase in temperature. In NTC thermistors, resistance
decreases as temperature increases. In PTC thermistors,
resistance increases as temperature decreases.
THS
Automotive
Technology
Electrical Circuits
Circuit control devices and how they function
• A circuit control device controls the amount of current
flowing through a circuit. It also ensures that current flows at
the proper time. A circuit control device performs one of
three essential functions.
The circuit control device opens or closes the circuit by
mechanical or electronic means.
The circuit control device relays a large rate of current by
means of a small current signal.
Lesson 1:
Components of
an Electrical Circuit
The circuit control device increases or decreases current
rate.
• The most common circuit control device is a switch.
The switch has two or more sets of contacts. Opening the
contacts is referred to as breaking the circuit. Closing the
contacts is called making the circuit.
THS
Automotive
Technology
Circuit control devices and how they function
Poles refer to the number of input circuit terminals and
throws refer to the number of output circuits.
• A single-input (pole), single-output (throw) switch is
called a single-pole, single-throw switch (SPST).
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
• A single-input (pole), double-output (throw) switch is
called a single-pole, double-throw (SPDT) switch.
• A multiple-input (pole), multiple-output (throw) switch
is called a multiple-pole, multiple-throw (MPMT)
switch.
Switches can be push-pull, rotary, or momentary on/off.
THS
Automotive
Technology
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Circuit control devices and how they function
The six different types of switches are the SPST, SPST
momentary contact, SPDT, MPMT, mercury, and
temperature-sensitive.
THS
Automotive
Technology
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Circuit control devices and how they function
• A relay is a remote-control switch that uses a small amount
of current to control a large amount of current. A standard
relay has a control circuit and a power circuit.
THS
Automotive
Technology
Electrical Circuits
Circuit control devices and how they function
The power source supplies current to the control circuit.
Current then flows through a switch and an electromagnetic
coil to ground.
The power source supplies current to the power circuit.
Current flows to an armature, which can be attracted by the
magnetic force on the electromagnetic coil.
• A solenoid is an electromagnetic switch that has a moveable
core to convert current flow into mechanical movement.
Lesson 1:
Components of
an Electrical Circuit
THS
Automotive
Technology
Circuit control devices and how they function
In the pulling-type solenoid, the magnetic field pulls the core
into a coil. A pull-in coil pulls the core into the coil, and a
hold-in coil holds the core in place.
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
In a push-pull-type solenoid, a permanent magnet is used for
the core. By changing current flow direction, the core is
pulled in or pushed out. This type of solenoid is used on
electric door locks.
THS
Automotive
Technology
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Circuit control devices and how they function
• Comfort and convenience luxuries are provided using
electronic devices and systems called solid-state electronics.
These work through the control of electricity and do not have
electromechanical parts.
Current flows through a semiconductor. This movement
produces an electrical signal that may be transmitted,
amplified, or utilized in special circuits in order to perform
logical decision-making functions.
• Semiconductors have the ability to act like conductors or
insulators. While their resistance is higher than conductors
like copper or iron, it is lower than insulators like glass or
rubber. Semiconductors have special electrical properties.
By mixing certain substances, conductivity can be increased.
Light, temperature, and mechanical pressure can alter
resistance.
By passing current through semiconductors, light is
produced.
THS
Automotive
Technology
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Circuit control devices and how they function
• The diode controls the direction of current flow but not the
rate of current flow. The diode acts as a one-way electron
check valve that allows current flow in one direction but
stops current flow coming from the other direction.
THS
Automotive
Technology
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Circuit control devices and how they function
• The zener diode is similar to the diode.
Under normal conditions, the zener diode allows current
flow in one direction and stops current flow in the opposite
direction up to a point.
If opposing current flow is forced hard enough, the zener
diode will break down, allowing current flow in either
direction.
When the opposing current flow decreases, the zener
diode again functions as a diode.
THS
Automotive
Technology
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Circuit control devices and how they function
• The light-emitting diode (LED) is a diode that produces
light. Transparent epoxy cases are produced with LEDs, so
they can emit the light they generate when forward biased.
Depending on how the material is doped, the color of the
light given off by a LED can be red, green, or infrared.
THS
Automotive
Technology
Circuit control devices and how they function
As in a diode, the LED allows current flow only in one
direction.
• The forward bias voltage drop is 1.5 volts to 2 volts,
which is much higher than a diode.
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
• The forward bias current through the LED must be
kept under control or damage will result.
Some advantages of LEDs are longer life, cooler operation,
lower voltage requirements, and the ability to produce the
same amount of light as an incandescent bulb while using
less power.
THS
Automotive
Technology
Electrical Circuits
Transistors and how they function
• Transistors are made from positive-type (P-type) and
negative-type (N-type) materials. They utilize the same
principles as the diode. Transistors have two positive/
negative junctions.
A transistor performs more functions than a diode, such as
operating as a solid-state switch or amplifier. When used in a
vehicle, the transistor is most commonly used as a switch.
• Transistors, such as the AC blower motor, are used as
amplifiers to control the speed of the electric motor.
Lesson 1:
Components of
an Electrical Circuit
• Transistors are used as solid-state switches to control
actuators, such as electronic fuel injectors.
THS
Automotive
Technology
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Transistors and how they function
• The three parts of a bipolar transistor are the emitter, base,
and collector.
The two types of bipolar transistors are the positivenegative-positive (PNP) and the negative-positive-negative
(NPN). Transistor type is determined by the type of material
used to make each of the three transistor parts.
THS
Automotive
Technology
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Transistors and how they function
• In the PNP transistor, the emitter is made from P-type
material, the base is N-type material, and the collector
is P-type material. In order for the PNP transistor to
operate, the emitter must be connected to negative, the
base to positive, and the collector to negative.
• In the NPN transistor, the emitter is made from N-type
material, the base is P-type material, and the collector is
N-type material. In order for the NPN transistor to
operate, the emitter must be connected to positive, the
base to negative, and the collector to positive.
PNP and NPN transistors function the same way. Both of
the transistors possess a forward-biased junction and a
reverse-biased junction.
THS
Automotive
Technology
Transistors and how they function
Current flow between the emitter and base controls current
flow between the emitter and collector.
• The emitter is the most heavily doped. It has the most
excess electrons or holes, depending on whether the
emitter is P-type or N-type material.
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
• The collector is doped slightly less than the emitter.
The base is thin with the fewest doping atoms.
As a result of doping, current flow in the emitter-collector
is much greater than in the emitter-base.
By regulating current at the emitter-base junction, the
amount of current allowed to pass from the emitter to
the collector is controlled.
THS
Automotive
Technology
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Transistors and how they function
THS
Automotive
Technology
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Integrated circuits
• An integrated circuit (IC) connects transistors, diodes,
capacitors, and resistors with conductors built onto one
silicon chip. Due to the compact design, the IC reduces
the number of contact junctions, cost of production, and
consumption of power. The IC is classified by the
number of parts included on one chip.
THS
Automotive
Technology
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Logic circuits
• Logic circuits consist of transistors combined in units called
gates. Gates are switches powered by voltage that process
signals logically based on digital on/off language.
NOTE: Logic circuits are represented by logic symbols to
aid in the understanding of the circuit. These logic symbols
are used to show the internal circuits of computers and
solid-state control modules and are helpful when analyzing
wiring damage.
THS
Automotive
Technology
Logic circuits
The AND gate is a circuit with two series switches. Both
switches must be closed for the circuit to operate.
Truth Table for AND Gate
Inputs
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Output
A
B
C
0
0
0
0
1
0
1
0
0
1
1
1
THS
Automotive
Technology
Logic circuits
The OR gate is a mechanical circuit with two parallel
switches. If either switch is closed or both are closed, the
circuit will operate.
Truth Table for OR Gate
Inputs
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Output
A
B
C
0
0
0
0
1
1
1
0
1
1
1
1
THS
Automotive
Technology
Logic circuits
The NOT gate inverts voltage so that output is opposite
of input.
Truth Table for NOT Gate
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Input
Output
A
C
1
0
0
1
THS
Automotive
Technology
Logic circuits
The NAND gate functions like an AND gate with an
opposite output. The output is on for all input conditions
unless there is voltage at both inputs.
Truth Table for NAND Gate
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Inputs
Output
A
B
C
0
0
1
0
1
1
1
0
1
1
1
0
THS
Automotive
Technology
Logic circuits
The NOR gate functions like an OR gate with an opposite
output. The output is on if there is no voltage at both
inputs.
Truth Table for NOR Gate
Electrical Circuits
Lesson 1:
Components of
an Electrical Circuit
Inputs
Output
A
B
C
0
0
1
0
1
0
1
0
0
1
1
0
THS
Automotive
Technology
Electrical Circuits
Logic circuits
The XOR gate is the exclusive OR gate that limits output
and is represented with an added curved line. The
exclusive feature requires that an even number of ones
produces a 0 (low output) while an odd number of ones
produces a 1 (high output).
Truth Table for XOR Gate
Inputs
Lesson 1:
Components of
an Electrical Circuit
Output
A
B
C
0
0
0
0
1
1
1
0
1
1
1
0